The user interface program will provide the solver routine with the following:

5 numbers of type integer:
------------------------
-the total number of elements 
-the total number of equivalenced nodes
-the number of entries in the fixed temperature boundary array
-the number of entries in the heat flux boundary array
-the number of entries in the heat generation boundary array

5 pointers to arrays of type double:
----------------------------------
-pointer to the elements array[0].
-pointer to the fixed array[0].
-pointer to the flux array[0].
-pointer to the gen array[0].
-pointer to the nodal temp array[0]. 

=======================================================================

-----------------------------------------
input to the solver code - elements array
-----------------------------------------

each Elements array entry contains:

int element_id, int node1_id,  int node2_id,  int type_of_element,  double resistance_value

type 0 = conduction
type 1 = convection
type 2 = radiation

eg.

1 1 2 0  1.00000000000000E+0001
2 2 3 0  1.00000000000000E+0001
3 2 4 0  1.00000000000000E+0001
4 2 5 0  1.00000000000000E+0001

------------------------------------------------------
input to the solver code - fixed, flux, and gen arrays
------------------------------------------------------

each of these arrays contain entries as: 

int node_id, int type_of_node, double user_supplied_temperature

type 0 = fixed
type 1 = flux
type 2 = gen

eg.

1 0  1.00000000000000E+0002
3 0  0.00000000000000E+0000
4 0  0.00000000000000E+0000
5 0  0.00000000000000E+0000

------------------------------------------------------
output from the solver code - nodal temperature array
------------------------------------------------------

each entry contains:

int node_id, double calculated_temperature

eg.

 1 1.000000e+002
 2 2.500000e+001
 3 0.000000e+000
 4 0.000000e+000
 5 0.000000e+000

=======================================================================

if you prefer the OpenGL typedefs, then: 

      int = GLuint
   double = GLdouble